1. Field of the Invention
The present invention relates to an integrated drive unit, or a wheel drive unit, and more specifically, to an improved integrated drive unit including an improved safety/parking brake and planet gear carrier.
2. Description of the Related Art
Integrated drive units have a single housing containing both a power input device and a transmission. The power input device can be, e.g., a hydraulic motor. Integrated drive units typically utilize axially oriented brake pads to provide a safety/parking brake. In many cases, stacks of interleaved brake discs are employed. When utilized with a hydraulic motor, brakes of this type are typically axially aligned with the motor barrel and extend from the end of the motor barrel opposite the motor pistons. The casing of the integrated drive must be of sufficient length to accommodate this type of a disc brake. Disc brakes of this type typically cannot withstand a dynamic stop, or xe2x80x9cdrive through.xe2x80x9d In a xe2x80x9cdrive throughxe2x80x9d case where the vehicle is at rest, with the emergency brake in operable (i.e., braking) position, and the vehicle is moved, the friction material will bum off and destroy the brake. Similarly, in an emergency situation when the vehicle is in motion, use of this brake to slow or stop the vehicle will cause its destruction.
Transmissions utilized within an integrated drive can include, e.g., planetary gears having planet carriers with cantilevered pins which rotatably support planet gears. Planet carriers of this type are unitary in construction and are typically forged or cast. Due to the one piece construction, these carriers can only accommodate one gear ratio. Thus, a new carrier is required for each desired gear ratio. Bearings such as, e.g., needle bearings are utilized to allow planet gears to rotate about the carrier pins of a planet carrier. To allow this relative movement without destruction of the pin, a hardened steel sleeve is press fit thereon, with the bearings being placed between the hardened steel sleeve and the planet gear. Fitting a hardened steel sleeve about the carrier pin of the planet carrier adds significant time and cost to the manufacturing process.
What is needed in the art is a safety/parking brake for use with an integrated drive unit which brake lessens the casing space required for the integrated drive unit and which can withstand dynamic braking activity.
What is further needed in the art is a planet carrier having a cantilevered carrier pin on which a planet gear rotates which does not require a hardened steel sleeve to be placed thereon and which will accommodate various gear ratios.
The foregoing shortcomings of the prior art are addressed by the present invention. The present invention provides an annular cone brake element which is affixed to the hydraulic motor barrel of an integrated drive unit. A brake piston encircles the hydraulic motor barrel and is selectively engageable with the cone brake element. In this arrangement, the integrated drive housing does not require extension to accommodate a plurality of brake pads axially aligned with and extending from the end of the hydraulic motor barrel opposite the hydraulic pistons. The cone brake element of the present invention is formed of a bronze-type powdered metal of sufficient durability to withstand dynamic braking.
The hydraulic motor is selectively connectable to a transmission including planetary gearing. The planetary gearing of the present invention includes a planet gear carrier comprised of a carrier plate having carrier pin bores positioned according to the desired gear ratio into which carrier pins may be placed and thereafter affixed to the carrier plate. The carrier pins of the current invention can be, e.g., laser welded to the carrier plate. The portion of the pin received into the pin bore of the carrier plate is formed of a soft steel to facilitate welding, while the portion of the pin onto which the planet gear will be mounted is locally hardened so as to eliminate the hardened steel sleeve which is utilized with carrier pins of the prior art. In an alternative embodiment, VESPEL sleeves are utilized to provide a bearing surface between the planet gear and the planet carrier. VESPEL is a rigid resin material available from E. I. DuPont de Nemours and Company.
In another form of the current invention, the planet gear carrier is an integral unit having both a carrier plate and a carrier pin formed from a one-piece forging. As described with respect to the two-piece carrier plate/carrier pin configuration, the portion of the pin onto which the planet gear will be mounted is locally hardened so as to eliminate the hardened steel sleeve which is utilized with carrier pins of the prior art. The hardened portion of the carrier pin can be hardened, e.g., by carbonization, or induction hardening. Generally, carbonization will be utilized to locally harden discrete carrier pins utilized with the two-piece carrier plate/carrier pin configuration, while induction hardening will be utilized to locally harden the integral planet gear carrier having both a carrier plate and a carrier pin formed from a one-piece forging. In one alternative embodiment, VESPEL sleeves are utilized in lieu of hardening the carrier pins.
The invention, in one form thereof, comprises an integrated drive unit including a fixed spindle and a rotatable hub connected to a wheel. The drive unit of this form of the current invention includes a hydraulic motor having a hydraulic motor barrel, a gear set selectively driven by the hydraulic motor, with the hub operably coupled to the motor through the gear set, and a cone brake affixed to the hydraulic motor barrel. The cone brake includes a plurality of friction surfaces lying on an exterior frusto-conical surface of the cone brake.
The invention, in another form thereof, comprises an integrated drive unit having an input shaft and a planetary gear set drivingly connected to the input shaft. In this form of the current invention, the planetary gear set includes a sun gear, at least one planet gear drivingly engaged with the sun gear, and a planet carrier rotatably supporting the at least one planet gear. The planet carrier includes a carrier plate, and a discrete carrier pin cantilevered from and affixed to the carrier plate. The carrier pin rotatably supports the planet gear.
The invention, in another form thereof, comprises an integrated drive unit having an input shaft and a planetary gear set drivingly connected to the input shaft. In this form of the current invention, the planetary gear set includes a sun gear, at least one planet gear drivingly engaged with the sun gear, and a planet carrier rotatably supporting the planet gear. The planet carrier of this form of the current invention includes an integral carrier pin which is locally hardened in an area contacting a bearing. The bearing is interposed between the carrier pin and the planet gear.
The invention, in another form thereof, comprises a method of forming a planet gear carrier for a planetary gear set. The method of this form of the current invention includes the steps of: providing a carrier plate having an aperture, providing a carrier pin, inserting the carrier pin into the aperture, and affixing the carrier pin to the carrier plate.
An advantage of the present invention is the ability to lessen the size of an integrated drive unit by utilizing a safety/parking brake which does not axially extend from the hydraulic motor barrel.
A further advantage of the present invention is the ability to provide a safety/parking brake which can withstand dynamic braking activity.
Another advantage of the present invention is the ability to provide a planet gear carrier having a cantilevered pin which does not require a hardened steel sleeve to be affixed to the pin.
Yet another advantage of the present invention is the ability to provide a planet gear carrier able to accommodate various gear ratios.